RFR: 8353218: Shenandoah: Out of date comment references Brooks pointers

[William Kemper]

Trivial change, comment only.

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Commit messages:
 - Fix trailing whitespace
 - Fix out of date comment

Changes: https://git.openjdk.org/jdk/pull/24304/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24304&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8353218
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/24304.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24304/head:pull/24304

PR: https://git.openjdk.org/jdk/pull/24304